Producing oxidation resistant lubricants



PRODUCING OXIDATION RESISTANT a LUBRICANTS JamesVan Dyck Fear, Media,Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation ofNew Jersey This invention relates to the production of oxidationresistant petroleum lubricating oils by processes involving catalytichydrogenation.

It is known in th art that hydrogenation ofpetr'oleum lubricating oilsis capable of improving the antioxidant additive response of the oils,as'indicated by the oxidation resistant characteristics of thelubricating oils containing anantioxidant additive. The mechanism ofsuch improvement has not however been fully understood. The presentinvention is based in part upon the recognition of animportant factorinvolved in the hydrogenation of lubricating oils which factor has notpreviously been recognized. As a result of this lack of recognition,prior art hydrogenations have not been conducted under the necessaryconditions for, producing superior oxidation resistant lubricantswithout undesirable side effects.

I" WhenJsaturated, i.e. 'nonaromatic, hydrocarbon constituentsf ofpetroleum lubricating oil are subjected to hydrogenation"conditions inthe' presence of aromatic hydrocarbons normally present in such oil,theuse of conditionsywhich ,most beneficially affect the additiveresponseof the saturatel constituents has undesirable efiec tson thearomatic constituents. The latter are conyerted to an excessive extentto undesirable product's, e.g.'.solid carbonaceous deposits, rather thanto products havingva beneficial effect on theproperties of the oil. Thepresent invention provides anovel manner of hydro genating petroleumlubricating oil components which producesrnaximum improvement ofsaturated hydrocarbons without accompanying undesirable effects. 7

The process according to the invention involves the separation of a.saturated hydrocarbon fraction from a petroleum lubricating oilinitially containing aromatic as well as saturated hydrocarbons. Thesaturated hydrocarbon fraction is then contacted with hydrogen in thepresence of a hydrogenation catalyst at a temperature within theapproximate range from 650 to 825 F. and

at a pressure preferably within the approximate range from 100 to 2500p.s.i.g., more preferably 500 to 1000 p.s.i.g. By hydrogenating in theabsence of aromatic constituents originally present, undesirable effectsthat wouldeotherwise berobtained under the conditions used are avoided,and it is made possible, in one embodiment, to hydrogenate the aromaticconstituents separately under different conditions producing additionalbeneficial results.

ticlesize within the approximate range from 4 to 30 mesh. The liquidhourly space velocity in such percolation is preferably within theapproximate range from 0.25 to 5 volumes of charge per volume ofcatalyst bed per hour. The hydrogen consumption is preferably within theapproximate range from 25 to 500 standard cubic feet of hydrogen perbarrelbf charge.

The saturated hydrocarbon fraction after subjection -to thehydrogenation conditions set forth above, has

improved additive response over that of the original lubricating oil andover that of the saturated hydrocarbon fraction prior to thehydrogenation. It is believed that this improvement is attributable atleast in part to the use of conditions which bring about, in addition toother desirable effects, some opening of a naphthene ring in saturatedhydrocarbons containing a plurality of naphthene rings. 1 v a It isdesirable in some instances to subject the hydrogenated saturatedfraction to a further refining step, e.g. a mild further hydrogenationor other suitable finishing treatment, in order to remove small amountsof undesirable cracked products formed during the previously describedhydrogenation. Mild hydrogenation gives generally superior results tothose obtained with other treatments, and is therefore preferred.

'The hydrogenated saturated hydrocarbon fraction containing'an alkylatedphenol or other antioxidant additive can be employed alone as alubricant in applications which require a high degree of oxidationresistance. Alternatively the saturated hydrocarbon fraction can beblended with a hydrogenated aromatic hydrocarbon fraction obtained asdescribed subsequently. Blends obtained in this manner also have verygood additive response resulting not only from the hydrogenation of thesaturated hydrocarbon fraction, but also from the hydrogenation of thearomatic hydrocarbon fraction under different conditions.

The conditions employed in the hydrogenation of the aromatic hydrocarbonfraction include temperatures within the approximate range from 450 to750 F. and

- preferably at least 550 F. The pressure is preferably Any knownmetallic hydrogenation catalyst can be employed in the hydrogenation ofthe saturated hydrocarbon fraction. .Such catalysts include thosecomprising the--metals,'cobalt, molybdenum, platinum, nickel, iron,palladium, etc. or oxides or sulfides of such metals. Preferably themetallic catalyst is associated with a suitable known carrier such asbauxite, alumina, silica gel, Silica-alumina composites, etc.

A preferredprocedure involves the percolation of the lubricating oil in'liquid phase through a bed of solid hydrogenation catalyst particlespreferably 'having'parwithin the approximate range from to 3000 p.s.i.g.Any suitable metallic hydrogenation catalyst such as those describedpreviously can be employed. The catao lyst may be the same as, ordifferent from, that employed in the hydrogenation of the saturatedhydrocarbons. Catalysts comprising cobalt molybdate are preferred.Preferred contacting technique involves percolation, as describedpreviously with respect to hydrogenation of the saturated fraction. Theliquid hourly space velocity is preferably within the approximate-rangefrom 0.5 to 10 and the hydrogen consumption within the approximate rangefrom 25 to 1000 standard cubic feet per barrel.

The hydrogenation of the aromatic fraction is performed, in thisembodiment, under conditions which inhibit excessive formation of solidcarbonaceous deposits. Factors contributing to this inhibition includelow temperature, high hydrogen pressure and high space rate. Thesaturated fraction, on the other hand, is hydrogenated under conditionsof greater severity, in the sense of conditions which would tend toresult in excessive formation of solid carbonaceous deposits ifperformed in the presence of the aromatic hydrocarbons. The saturatedfraction is not necessarily hydrogenated at a higher temperature, lowerhydrogen pressure, and higher space rate than the aromatic fraction;however, the conditions in the saturated hydrocarbon hydrogenation whichwould tend to increase carbonaceous products in' the presence ofaromatic hydrocarbons, are more predominant, as compared with thoseconditions which would tend to decrease such products, than in thearomatic hydrocarbon Patented Apr. 18, 1961' hydrogenation. In the lightof the present specification,

a person skilled in the art can determine such combinations ofconditions. Preferably, the temperature in the hydrogenation of thesaturated fraction is higher than inthe hydrogenation of the aromaticfraction, e.g.; atv

least 25 F. higher.

The hydrogenated aromatic hydrocarbon fraction has improved oxidationresistance as compared with the aromatic fraction prior to thehydrogenation. The product also has improved viscosity index and color.

The hydrogenated aromatic fraction can be blended with the hydrogenatedsaturated fraction in thesame proportions as. in the originallubricating oil. Alternatively the fractions can be blended in differentproportions.

Usually, where blends are employed, each component.

comprises at least 10 volume percent of the blend.

The original separation of a saturated hydrocarbon fraction from the oilcan be carried out in any suitable manner. Preferably the separationinvolves the use of a selective adsorbent such as silica gel, activatedalumina,v

activated carbon, etc. Preferably the adsorbent is employed in the formof particles having size within the approximate range from 10 to 300mesh, more preferably 25 to 200 mesh. The temperature employed in suchseparation is preferably within the approximate range from 50 to 300 F.The separation is preferably performed in the presence of a suitablediluent such as petroleum naphtha. The contacting of the lubricating oilwith the selective adsorbent is preferably followed by contacting theadsorbent, containing adsorbed constituents of the oil, with a suitableliquid desorbent such as benzene, xylene, acetone, etc. Variousdesorbents for use in processes for separating petroleum fractionsaccording to hydrocarbon type on a selective adsorbent are well known inthe art, and any of the known desorbents can be employed for the purposeof the present invention, the separation according to hydrocarbon typebeing in itself a conventional operation.

The saturated hydrocarbon fraction obtained in the separation preferablycontains less than aromatic hydrocarbons. Similarly the aromaticfraction preferably contains less than 5% of saturated hydrocarbons.Aromatic hydrocarbons, for purposes of the present disclosure, arehydrocarbons which contain one or more aromatic rings in the molecule.

If desired, the separation by means of selective adsorbent can beconducted in such manner that a small fraction, .e.g. about 5%, of theoil is retained on the adsorbent after the removal of the aromaticfraction. This 5% represents an undesirable material which is preferablyexcluded from the aromatic fraction.

If desired, the separation of the original lubricating oil can beperformed by a solvent extraction process employing well known solventsfor aromatic hydrocarbons, e.g. furfural, phenol, etc. However the useof an adsorptiondesorption operation is preferred in that it provides asharper separation between aromatic and saturated (i.e. non-aromatic)constituents.

It is within the scope of the invention to separate the original oilinto a plurality of saturated hydrocarbon fractions having differentcomposition, and hydrogenateone or more of such saturate fractionsseparately from the other components of the oil. It is also within thescope of the invention to separate the original oil into a plurality ofaromatic fractions having different composition and hydrogenate one ormore of such fractions separately from other constituents of the oil.

In one embodiment, a raffinate produced in solvent .extraction, andstill containing a substantial quantity, e.g. about 15 weight percent,of aromatics, is separated by adsorbent-desorption technique into asubstantially aromatic-free saturated hydrocarbon fraction and asubstantially saturate-free aromatic hydrocarbon fraction. Therespective fractions are then hydrogenated under conditions previouslyindicated as suitable for each. The exseconds.

tract produced in the solvent extraction is preferably not used in thefinal lubricating oil, though it is within the scope of the invention toinclude it, preferably after being hydrogenated under the conditionspreviously set forth for hydrogenation of aromatic fractions.

The charge oil according to the invention is a petroleum lubricating oilhaving Saybolt Universal viscosity at F. of at least 50 seconds, andmore preferably at least 100 Usually the lubricating oil will not have aviscosity of more than about 300 Saybolt Universal secondsat 210 F.Preferably not more than 5 volume percent of the charge oil has boilingpoint below 600 F.

The following example illustrates the invention:

Naphthenic crude oil having viscosity-gravity constant of about 0.89 isdistilled to produce an acid-free distillate having Saybolt Universalviscosity at 100 F. of 100 seconds. 200 parts by weight of thisdistillate are percolated through 1200 parts by weight of 28 to 200 meshsilica gel inan elongated column. Following the introduction of thelubricating oil distillate together with n-pentane diluent into the gelcolumn, additional n-pentane is introduced into the column in order todesorb saturated components ofthe original oil. The efiluent pentanecontaining saturated hydrocarbons is distilled in order to removepentane and obtain a saturated'hydrocarbon fraction constituting about55% of the original oil; This fraction contains less than 1% aromatichydrocarbons. Following the pentane, a mixture of 75% benzene and 25%pentane is introduced into the gel column to desorb aromatichydrocarbons. The effluent solvent containing aromatics is distilled toremove solvent and obtain as residuean aromatic fraction comprisingabout 40% of the original oil. 7

The saturated hydrocarbon fraction is contacted with a solidhydrogenation catalyst comprising about 12.5% cobalt molybdate on analumina carrier. The saturated fraction is percolated through a bed ofthe catalyst at a temperature of 675 F; and pressure of 800 p.s.i.g. andliquid hourly space velocity of one. The hydro. genated product hasincreased oxidation resistancetinhibited) over that of the saturatesprior. to hydrogenation; as determined by a standard test involvingdetermination of the lengthof time elapsed before the oil, containing0.4% of-added 2,6-ditertiary butyl p-cresol as inhibitor, absorbs orreacts with a predetermined'amount of oxygen. The product is furtherincreased in oxidation resistance, as determined by this test, bysubjection to further'hydrogenation at 600 F. and 500 p.s.i.g. andliquid hourly spacevelocity of one, employing the same catalyst as inthe preceding hydrogenation.

The aromatic hydrocarbon fraction is percolated at 600 F. and 500p.s.i.g. through a bed of solid'hydrotgenation catalyst comprising 20%molybdenum disulfide on a bauxite carrier. The liquid hourly spaceveloc-. ityisone. The hydrogenated aromatic fraction has-ine creasedoxidation resistance, as determined by the standardtest referred toabove, over the aromatic fraction prior to hydrogenation.

The saturated hydrocarbon fraction with inhibitor can be employed aloneas a lubricating oil or in a blend with the hydrogenated aromatic,fraction, the blendfor example containing about 40 parts of hydrogenatedaromatic fraction and 55 parts of hydrogenated saturate fraction. Thehydrogenated saturate fraction, and also the blend thus obtained havesuperior oxidation resistance to an oil obtained by hydrogenating theoriginal lubricating oil distillate under typical conditions such asthose used in hydrogenating the aromatic fraction.

Hydrogenation ofv the aromatic and saturated fractions separately avoidssubjection of the separated aromatic hydrocarbons to the hightemperature conditions required in the hydrogenation of the saturatedfraction. The aromatic hydrocarbons tend to undergo undesirablereactions, such as coke-forming reactions, at the higher temperatures,

In another embodiment of the invention, the separation by means ofsilica gel and desorbents is performed in such manner that the efiiuentdesorbent containing aromatic constituents is divided into twofractions. The earlier aromatic effiuent desorbent fractions arerecovered separately from the later efiiuent desorbent fractions Uponremoval of desorbent from the earlier desorbent fractions, a hydrocarbonfraction is obtained constituting a mononuclear aromatic hydrocarbonconcentrate. From the later desorbent fractions, polynuclear aromatichydrocarbons are obtained. The mononuclear aromatic concentrate, whichconstitutes about 20% of the original oil, is hydrogenated at theconditions set forth above for the hydrogenation of the aromaticfraction. The bydrogenated material can be used alone as a lubricant orblended with hydrogenated saturates or with the remainder of thearomatics (hydrogenated or unhydrogenated) or in any other desiredcombination.

Generally similar results to those obtained above are obtained in asimilar treatment of lubricating oils derived from paraflinic orparaffinic-naphthenic base crudes. The latter types of crude generallycontain lesser amounts of aromatic hydrocarbons than in the case ofnaphthenic crudes, but the results obtained are qualitatively the same.Generally similar results are also obtained employing otherhydrogenation catalysts such as those referred to previously.

The process according to the invention provides a product which isparticularly susceptible to improvement by known antioxidant additivesgenerally. Examples of suitable additives which are advantageously addedto the product are the alkylated phenol oxidation inhibitors, which arewell known as a class in the prior art, e.g. the polyalkyl aryl hydroxycompounds such as 2,6-ditertiary butyl-4-methyl phenol,2,4-dimethyl-6-tertiary octyl phenol, pentamethyl phenol, pentaethylphenol, tritertiary butyl phenol, 2-isopropyl-4,6-dimethyl phenol,Z-tertiary butyl-4,6-dimethyl phenol, 2-tertiary amyl-4,6-dimethylphenol, 4-methyl-2,6-diisopropyl phenol, 2,6-ditertiary amylphenol-4-tertiary butyl phenol, 2,4,6-triisopropy1 phenol, etc. Otherknown types of oxidation inhibitors can also be employed, for examplevarious compounds of sulfur, phosphorus or sulfur and phosphorus,various amines, etc. Examples of such oxidation inhibitors aresulfurized lauryl oleate, sulfurized terpenes, alkyl sulfides, tributylphosphite, lecithin, diphenyl amine, etc.

The invention claimed is:

1. Process for producing oxidation resistant lubricants which comprisesseparating petroleum lubricating oil into a saturated fraction and anaromatic fraction, contacting the saturated fraction with hydrogen inthe presence of a. metallic hydrogenation catalyst at a temperature of650 to 825 F., contacting the aromatic fraction with hydrogen in thepresence of a metallichydrogenation catalyst at a temperature of 450 to750 F., the severity of the latter contacting being less than that ofthe firstnamed contacting, and blending the hydrogenated aromaticfraction withthe hydrogenated saturated fraction.

2. Process for producing oxidation resistant lubricants which comprisesseparating distillate petroleum lubricating oil into a saturatedfraction andan aromatic fraction, contacting the saturated fraction withhydrogen in the presence of a metallic hydrogenation catalyst at atemperature in the range from 650 to 825 F., a pressure in the rangefrom to 2500 p.s.i.g. and a liquid hourly space velocity in the rangefrom 0.25 to 5, and contacting the aromatic fraction with hydrogen inthe presence of a metallic hydrogenation catalyst at a temperature inthe range from 450 to 750 F., a pressure in the range from to 3000p.s.i.g., and a liquid hourly space velocity in the range from 0.5 to10, and blending the hydrogenated saturated fraction with thehydrogenated aromatic fraction.

3. Process for producing oxidation resistant lubricants which comprisesseparating petroleum lubricating oil into a saturated fraction and aconcentrate of mononuclear aromatic hydrocarbons, contacting thesaturated fraction with hydrogen in the presence of a metallichydrogenation catalyst at a temperature of 650 to 825 F., contactingsaid concentrate with hydrogen in the presence of a metallichydrogenation catalystat a temperature of 450 to 750 F., the severity ofthe latter contacting being less than that of the contacting of thesaturated fraction with hydrogen, and blending the hydrogenatedconcentrate with the hydrogenated saturated fraction.

4. Process for producing oxidation resistant lubricants which comprisesseparating petroleum lubricating oil by selective adsorption treatmentwith a granular solid adsorbent capable of producing a saturated productcontaining less than 5 percent of aromatic hydrocarbons, thereby toobtain a saturated fraction containing less than 5 percent of aromatichydrocarbons and an aromatic fraction, and contacting the saturatedfraction with hydrogen in the presence of a metallic hydrogenationcatalyst at a temperature of 650 to 825 F.

References Cited in the file of this patent UNITED STATES PATENTS1,934,063 Haslam Nov. 7, 1933 1,949,231 Young Feb. 27, 1934 2,461,454Toettcher Feb. 8, 1949 2,627,495 Lanning Feb. 3, 1953 2,767,131 Jezl.'Oct; 16, 1956 2,768,129 Know Oct. 23, 1956 2,848,384 Fear Aug. 19,1958 2,875,145 Annable et al Feb. 24, 1959 2,898,286 Kleinholz Aug. 4,1959

1. PROCESS FOR PRODUCING OXIDATION RESISTANT LUBRICANTS WHICH COMPRISESSEPARATING PETROLEUM LUBRICATING OIL INTO A SATURATED FRACTION AND ANAROMATIC FRACTION, CONTACTING THE SATURATED FRACTION WITH HYDROGEN INTHE PRESENCE OF A METALLIC HYDROGENATION CATALYST AT A TEMPERATURE OF650 TO 825*F., CONTACTING THE AROMATIC FRACTION WITH HYDROGEN IN THEPRESENCE OF A METALLIC HYDROGENATION CATALYST AT A TEMPERATURE OF 450 TO750*F., THE SEVERITY OF THE LATTER CONTACTING BEING LESS THAN THAT OFTHE FIRSTNAMED CONTACTING, AND BLENDING THE HYDROGENATED AROMATICFRACTION WITH THE HYDROGENATED SATURATED FRACTION.